In a conventional electronic oven, formed in the upper wall of the cavity is an opening for directing infrared rays radiated from food heated in the cavity to the infrared detector element disposed above the cavity upper wall. However, an atmosphere containing a pollutant such as vapor and oil drops derived from the food heated in the cavity also passes through this opening. This presents a problem in that the infrared converging means, the infrared detector element or the like disposed above the opening are easily contaminated by such a pollutant.
In order to eliminate such problem, following proposals have been made:
(1) To bring an infrared ray permeable filter in close contact with said opening; and
(2) To slide a shutter for closing said opening during the time the temperature measurement operation is not performed.
Apparatus of the type (1) above-mentioned is economical and highly reliable because of the absence of mechanical movements required therein, but the filter should be cleansed often according to frequency of use, which is very troublesome.
In apparatus of the type (2) above-mentioned, vapor and oil drops, etc. stick to the space between the opening and the shutter and become something like adhesives, so that a considerable force is required for sliding the shutter across the opening.